The present invention relates generally to the field of display devices, such as liquid crystal displays ("LCDs"), cathode ray tubes ("CRTs"), and similar display devices. More specifically, the present invention relates to methods of and apparatuses for reducing the infrared loading (e.g., solar loading from the sun) on such display devices by using a reflective material to reflect infrared energy.
A "display" is an image output device that provides information to an observer in a visible form. A "liquid crystal display" ("LCD") is a display device that includes a liquid crystal cell with a light transmission characteristic that can be controlled in parts of the cell by an array of light control units to cause presentation of an image. A "liquid crystal cell" is an enclosure containing a liquid crystal material. An "active-matrix liquid-crystal display" ("AMLCD") is an LCD in which each light control unit has a nonlinear switching element that causes presentation of an image segment by controlling a light transmission characteristic of an adjacent part of the liquid crystal cell. An LCD can have a plurality of electrically-separated display regions, each display region also being known as a display cell, or when the regions designate a small portion of the display, each display region is known as a "pixel." Each pixel in a high density display matrix, such as for LCDs, requires its own active (switching element) driver (e.g., a thin film transistor).
In recent years, LCD devices have become more popularly used in avionics and ground vehicle displays because of the low power consumption, high reliability, high ambient readability, and compact packaging of LCDs. Also, personal computers, portable game machines, hand-held devices, wrist watches, gas station pumps, and numerous other devices requiring a visual interface often use LCDs to display data. All of these types of display devices and many others are likely to be exposed to the sun or radiant energy thus creating a thermal rise due to solar exposure thereon (solar loading).
In most display devices that are subject to receiving radiant energy, the following problems are posed. The display device often experiences a temperature rise of the display device due to solar loading or other radiant energy sources. For example, it is possible for a display device to experience solar loading on its surface up to 116 W/ft.sup.2 depending on its application. This solar loading problem is intensified when cooling methods, such as forced cooling air, are unavailable. As a result, the display device can be permanently damaged, such as is the case with polarizers and adhesives associated with LCDs when exposed to temperatures in excess of 100.degree. C. Also, sometimes the liquid crystal material of an LCD device "clears" (exceeds its operating capability due to the temperature of the liquid crystal). When liquid crystal material "clears" it transitions from the nematic phase and becomes anistropic, effectively randomizing the birefringent characteristic of the liquid crystal material, which takes time and temperature changes to return to its operating state.
To date, some attempts have been directed toward remedying the solar loading phenomena and its associated problems. With regard to LCDs, one proposed solution is to increase the limiting temperature of the liquid crystal materials and polarizers. This approach alleviates the problem, but the availability of these materials is limited. Also, this approach is not practical for commercially-available liquid crystal materials due to a significant cost factor. Another proposed solution has been to force cool air over the exterior face of the display device, i.e., the display device surface that is exposed to the viewer. This approach is practical only when cooling air is available, which is not always the case. Yet another workaround has been the use of a cover to protect the display device from temperature increases due to solar loading. Thus, a need exists to reduce the solar loading on display devices that are subjected to a thermally-challenging environment. Accordingly, the present invention discloses a method of and apparatus for reducing the solar loading on display devices.